The Shoe-Fitting Fluoroscope

Sam Birer
March 7, 2011

Introduction

Fluoroscopy is a technique where a physician or
technician images a part of a patient's body using X-rays and a
fluorescent screen. [1] The fact that X-rays are ionizing radiation
means that modern doctors must carefully weigh the costs and benefits of
the procedure, as it represents a significant amount of radiation
exposure. [2] This safety concern was not always taken into account, and
for many years fluoroscopy was used to fit shoes properly, especially in
children. The U.S. Patent for the shoe-fitting fluoroscope was issued
in 1927, and it was a common item in shoe stores in the United States
through the 1950s. [3] (They remained in use in Britain until the
mid-1970s.) Safety regulations were introduced as an informal industry
standard in 1946, with at least one state passing similar regulations
into law, although there is significant data demonstrating that these
regulations were rarely followed. [3,4] The majority of machines
surveyed by one study in 1950 had a median radiation output of almost
twice the recommended limit, with one machine putting out very nearly
4.5 times more roentgens/minute than the industry limit. [4]

Radiation Data and Exposure Levels

Regulation of shoe-fitting fluoroscopes was for the
most part informal, but from 1946 on it was recommended that a person
receive no more than 2 roentgens per 5 second exposure (24 R/min) and
use a fluoroscope no more than 20 times per year. Despite this
standard, most machines were fitted with dials that allowed the time
interval to be ranged from 5-45 seconds, with the reportedly most
frequent setting at 20 seconds. [3] Although roentgens do not convert
exactly into grays, which are the standard unit of radiation absorbance,
for soft tissue absorption 1 roentgen is usually approximated to be
0.00876 Gy. [1] Assuming that industry standards were followed precisely
and the machine was used for no more than 20 seconds per usage, this
works out to a standard limit of 0.0744 Gy per visit, or 1.4883 Gy per
year. To put this number in perspective, the LD50 for a single exposure
event of ionizing radiation without medical intervention in adults is
thought to be 4.5 Gy [5], and the current U.S. occupational annual
radiation exposure limit is 0.05 Gy. [6] While it may be difficult to
imagine a person getting fitted for shoes 20 times in a single year,
machines varied so greatly in their actual radiation output and
operation that a total annual absorption of > 1.65 Gy is not entirely
infeasible. A 1950 survey of machines put the median output of
radiation for these fluoroscopes at 40 R/min, with a mean and maximum of
38.7 and 107 R/min, respectively. [4] A machine set at 40 R/min would
give a dose of 0.1240 Gy per 20 second imaging, or up to 2.480 Gy/year.
A hypothetical worst-case scenario machine set at 107 R/min for 45
seconds would give a dose of 0.7465 Gy per use, well into the range
where it could start giving acute radiation poisoning from a single
visit!

Radiation Data and Exposure Levels

The impact of the shoe-fitting fluoroscopes on the
health of their users is not really known. While it is known that
radiation is a significant carcinogen, there do not appear to have been
any long-term studies about how these machines have affected the cancer
rates of users or otherwise adversely affected them, and such a study
would be very difficult to control properly. Some studies have pointed to
specific cancers as the product of shoe-fitting fluoroscopes [3], but given
that there were nearly 10,000 machines in the United States alone, and
countless customers who tried them but no data to support an
extraordinarily high cancer rate among the population the right age to
have used them, it appears that the fluoroscopes did not have a
significant public health impact. [7] While it is inarguable that
radiation can pose a major health risk, it is a testament to the
resilience of the human body that people could repeatedly be exposed to
such high level of radiation and as a group continue to live without
being measurably worse for the wear.